The rapid growth of computer technology and the proliferation of data terminals among widely scattered telephone company subscribers has given rise to a need to provide efficient means for interconnecting these subscribers. The difficulty resides in the fact that the subscribers' terminals operate at widely varying data rates. In the past, this suitation has typically been handled by either providing each subscriber with a separate transmission link for each different terminal speed, or by using a common, untimed digital line for all the terminals. The former solution is clearly uneconomical. The latter solution is equally unsatisfactory in that the errors in a repeatered but untimed system tends to accumulate, thus limiting the length of line over which data can be efficiently transmitted.